PKC plays an important role in transmembrane signal transduction and participates in a variety of cellular processes. including proliferation, differentiation, release of hormones and neurotransmitters. It consists of a large family of at least nine different isoenzymes. During the past year we have studied the tissue distribution of new members of the PKC family, including the delta, zeta, epsilon isoforms. Our observations indicate that each of these isoenzymes exhibits a specific tissue and cellular distribution in the body. The delta isoform is widely distributed in the central nervous system while the zeta is associated with endocrine organs. PKC delta is present mostly in neurons that are involved in the transformation of sensory information from the periphery but is also present in a subset of motoneurons. While in most neurons it is located in the cytoplasm, in thalamic neurons PKC delta is present in nuclei of these cells. The immortalized LHRH cell line also produces some of PKC isoenzymes; thus, they provide an excellent model for studying basic cellular events.